Researchers at the University of Michigan believe they have proven that a common household chemical can disrupt thyroid function.

BPA — bisphenol-A — is a controversial type of chemical compound called a phthalate, used in solvents and plastics found in many household items, including plastic water bottles and the linings of canned food.

A growing number of scientists and government agencies question its safety.

Canada has declared BPA a toxic substance, and its use is banned in baby bottles in this country and in the European Union.

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It is thought to play a role in health problems ranging from obesity and erectile dysfunction to neurological disorders and some types of cancer.

They concluded that higher concentrations of BPA are associated with decreases in certain thyroid hormones, which regulate a number of body functions including metabolism and reproduction.

While the difference between those with the highest exposure to phthalates and those with the lowest was not more than 10%, "If you think about the entire population being exposed at this level, you'd see many more thyroid-related effects in people," said the study's lead author, John Meeker.

The findings appear in the journal Environmental Health Perspectives.

In a separate study, University of Cincinnati researchers found that products marketed as "BPA-free" alternatives are, for the most part, living up to their claims.

Professor Scott Belcher and colleagues found that stainless steel bottles and co-polyester-lined aluminum bottles don't release BPA; however, aluminum bottles lined with epoxy-based resins still result in BPA contamination of the liquids stored inside them.